Two Chronic Stress Models Based on Movement Restriction in Rats Respond Selectively to Antidepressant Drugs: Aldolase C As a Potential Biomarker.

BACKGROUND: Clinically depressed individuals respond to different types of antidepressants, suggesting that different neurobiological mechanisms may be responsible for their depression. However, animal models to characterize this are not yet available. METHODS: We induced depressive-like behaviors in rats using 2 different chronic stress models: restraint in small cages or immobilization in adaptable plastic cones. Both models increased anxiety responses evaluated by novelty-suppressed feeding and the elevated plus-maze; increased learned helplessness evaluated by the tail suspension and forced swimming tests; and increased anhedonia evaluated by the sucrose preference test. RESULTS: We assessed the ability of 2 different types of antidepressants to ameliorate depressive-like behaviors. We administered the serotonin reuptake inhibitor fluoxetine or the noradrenaline reuptake inhibitor reboxetine once daily for 28 days to rats that received either chronic restraint or immobilization stress, or no stress. Behavioral analysis revealed that fluoxetine ameliorated depressive-like behaviors when induced by chronic restraint stress, whereas reboxetine ameliorated these behaviors when induced by chronic immobilization stress. To further test biological differences between both models, we evaluated the levels of Aldolase C, an enzyme expressed by forebrain astrocytes that is regulated by antidepressant treatment, in the cerebrospinal fluid: chronic restraint stress, but not immobilization stress, increased the levels of Aldolase C. Moreover, the presence of astrocyte-derived Aldolase C-GFP in the cerebrospinal fluid indicates its central origin. CONCLUSIONS: Two stress paradigms induced depressive-like behaviors that were sensitive to different antidepressant treatments. Biomarkers such as Aldolase C could help determine optimal antidepressant treatments for clinically depressed patients.

The glycolytic enzyme aldolase C is up-regulated in rat forebrain microsomes and in the cerebrospinal fluid after repetitive fluoxetine treatment.

The antidepressant drug fluoxetine is widely used for the treatment of a broad range of psychiatric disorders. Its mechanism of action is thought to involve cellular adaptations that are induced with a slow time course after initiation of treatment. To gain insight into the signaling pathways underlying such changes, the expression levels of proteins in a microsomal sub-fraction enriched in intracellular membranes from the rat forebrain was analyzed after two weeks of treatment with fluoxetine. Proteins were separated by two-dimensional gel electrophoresis, and the differentially regulated protein spots were identified by mass spectrometry. Protein network analysis suggested that most of the identified proteins could potentially be regulated by the insulin family of proteins. Among them, Fructose-bisphosphate aldolase C (AldoC), a glycolytic/gluconeogenic enzyme primarily expressed in forebrain astrocytes, was up-regulated 7.6-fold. An immunohistochemical analysis of the dorsal hippocampus revealed a robust decrease (43±2%) in the co-localization of AldoC and the astrocyte marker GFAP and a diffuse staining pattern, compatible with AldoC secretion into the extracellular space. Consistently, AldoC, contained in an exosome-like fraction in astrocyte conditioned medium, increased significantly in the cerebrospinal fluid. Our findings strongly favor a non-canonic signaling role for AldoC in cellular adaptations induced by repetitive fluoxetine treatment.

Augmentation of the behavioural effects of desipramine by repeated immobilization stress.

The present report provides evidence that repeated immobilization stress (RIS) induced a noradrenergic-dependent depressive-like behaviour and an augmented behavioural response to desipramine (DMI), a noradrenaline reuptake inhibitor (NRI), in the forced swimming test (FST). The present results show that RIS decreased the baseline of climbing behaviour in the FST. Whereas subchronic administration of DMI (10mg/kg, three times in a 24h period) induced a significantly higher increase in climbing behaviour on repeatedly stressed rats compared to controls. The results also show that the concomitant administration of the low dose of DMI (3mg/Kg) during the RIS fully prevented the decrease of climbing behaviour induced by RIS, without exerting behavioural effects in control rats, further supporting an augmented response to the DMI antidepressant effects in the repeatedly stressed rats. In conclusion, our data indicate that RIS not only changes the behavioural responses in the FST but also increases the antidepressant effects of DMI.

Desipramine prevents the sustained increase in corticotropin-releasing hormone-like immunoreactivity induced by repeated immobilization stress in the rat central extended amygdala.

Clinical and experimental studies have shown that the activation of corticotropin-releasing hormone (CRH) and noradrenergic systems mediate stress-induced anxiety. Repeated immobilization stress (RIS) has been shown to induce long-lasting anxiety behavior and changes in noradrenaline turnover. The present work was aimed at studying the effect of RIS on the in situ expression of CRH-LI in the central extended amygdala and paraventricular nucleus of the hypothalamus (PVN). Our results showed that RIS for 15 days induces a significant increase of CRH-LI expression in the central extended amygdala. The increase in CRH-LI expression in the central extended amygdala was sustained even after a 25-day stress-free period. The concomitant administration of desipramine (DMI), a specific noradrenaline uptake inhibitor, fully prevented the RIS-induced increase in CRH expression. RIS also induced an increase of CRH-LI expression in the PVN that was prevented by the concomitant DMI administration. In contrast to the sustained effect observed in the central extended amygdala, the RIS-induced increase of CRH-LI expression in the PVN was nonlasting. DMI administration also prevented the RIS-induced increase of adrenal gland weight. The present findings showing that RIS induces a sustained increase of CRH expression in the central extended amygdala suggest that the repeated activation of CRH neurons and CRH receptors in the central extended amygdala may underlie the long-lasting anxiety behavior induced by RIS. Further studies should address the mechanisms involved in the effect of DMI and its eventual relevance in the therapeutic actions of DMI.

Expression of scavenger receptors in glial cells. Comparing the adhesion of astrocytes and microglia from neonatal rats to surface-bound beta-amyloid.

Astrocytes and microglia associate to amyloid plaques, a pathological hallmark of Alzheimer disease. Microglia are activated by and can phagocytose beta-amyloid (Abeta). Scavenger receptors (SRs) are among the receptors mediating the uptake of fibrillar Abeta in vitro. However, little is known about the function of the astrocytes surrounding the plaques or the nature of their interaction with Abeta. It is unknown whether glial cells bind to nonfibrillar Abeta and if binding of astrocytes to Abeta depends on the same Scavenger receptors described for microglia. We determined the binding of glia to Abeta by an adhesion assay and evaluated the presence of scavenger receptors in glial cells by immunocytochemistry, immunohistochemistry of brain sections, and immunoblot. We found that astrocytes and microglia from neonatal rats adhered in a concentration-dependent manner to surfaces coated with fibrillar Abeta or nonfibrillar Abeta. Fucoidan and poly(I), known ligands for SR-type A, inhibited adhesion of microglia and astrocytes to Abeta and also inhibited Abeta phagocytosis. In contrast, a ligand for SR-type B like low density lipoprotein, did not compete glial adhesion to Abeta. Microglia presented immunodetectable SR-BI, SR-AI/AII, RAGE, and SR-MARCO (macrophage receptor with collagenous structure, a member of the SR-A family). Astrocytes presented SR-BI and SR-MARCO. To our knowledge, this is the first description of the presence of SR-MARCO in astrocytes. Our results indicate that both microglia and astrocytes adhere to fibrillar and nonfibrillar Abeta. Adhesion was mediated by a fucoidan-sensitive receptor. We propose that SR-MARCO could be the Scavenger receptor responsible for the adhesion of astrocytes and microglia to Abeta.

Adrenalectomy decreases corticotropin-releasing hormone gene expression and increases noradrenaline and dopamine extracellular levels in the rat lateral bed nucleus of the stria terminalis.

The bed nucleus of the stria terminalis (BNST) has a high density of corticotropin-releasing hormone (CRH)-containing neurons that are significantly innervated by noradrenergic and dopaminergic nerve terminals. This limbic structure is involved in the extrahypothalamic response to stress. The purpose of the present work is to study whether the absence of glucocorticoids, induced by a long-term adrenalectomy, regulates CRH gene expression and noradrenaline and dopamine extracellular levels in the rat BNST. The results showed that adrenalectomy decreases CRH mRNA in the dorsal lateral BNST but not in the ventral lateral BNST. Adrenalectomy also decreases CRH-like immunoreactivity both in BNST subnuclei and in the central nucleus of the amygdala. In addition, adrenalectomy significantly increases noradrenaline and dopamine extracellular levels in the lateral BNST. The present results suggest that adrenalectomy regulates CRH gene expression and noradrenaline and dopamine extracellular levels in the BNST in an opposite way. Thus, the present study adds novel evidence further supporting that the BNST and the central nucleus of the amygdala form part of an adrenal steroid-sensitive extrahypothalamic circuit that has been involved in fear and anxiety responses and in clinical syndromes such as melancholic depression, posttraumatic stress disorders, and addiction.